1. Technical Field
The present disclosure relates to improvements in the design of a low pressure relief valve and methods of manufacturing, assembling and calibrating same.
2. Discussion of the Related Art
Known low pressure relief valves relieve pressures of, for example, below 500 psi in gas and/or liquid systems. Referring to FIG. 1, a known type of low pressure relief valve 10, such as the 500 series relief valve manufactured by Circle Seal Controls, Inc., has a compact design, and includes a mushroom type poppet 11, with an O-ring seal 12, spring 13, guide spider 14, and adjusting nut 15 under the head of the poppet 11.
However, in order to assemble the valve 10 and set the pressure, the components thereof must be assembled into the valve body 16 and then the adjusting nut 15 must be screwed onto the threaded poppet shaft. This nut 15 must then be spun up and down on the poppet shaft to adjust the set pressure. This assembly and pressure adjustment process is tedious and time consuming.
The valve 10 employs the mushroom style poppet 11 with the O-ring seal 12 that is dropped into the discharge end of the valve body 16. To contain fluid at pressures below set pressure, the O-ring 12 mates when the valve is closed, with a tapered sealing area 17 on the body 16. This tapered sealing area 17 serves as a guide for the poppet 11, but only when the valve 10 is closed.
Into the other end of the valve body, a spring 13, and a guide spider 14 is assembled and screwed onto the threaded poppet shaft. This guide spider 14 is threaded and is rotated relative to the poppet 11 in order to vary the spring force, which establishes the set pressure of the valve 10. Lastly, the adjusting nut 15 is screwed onto the poppet 11 to lock the guide spider 14 to the poppet 11.
Once assembled, the valve 10 is placed in a test fixture and fluid (liquid or gas) is introduced at a prescribed flow rate, and the pressure is observed. With this configuration, the relief pressure cannot be adjusted while fluid flow is being applied to the valve 10, because an adjusting wrench to turn the adjusting nut 15 will disturb the force balance between the piston area of the poppet and the poppet spring 13. To adjust the relief pressure setting of the valve 10, the poppet 11 must be held firmly against the seat to prevent rotating the poppet 11, while the guide spider 14 is rotated. Fluid flow is again introduced into the valve 10 to see how close the pressure is to the design requirement. This process is then repeated as many times as necessary until the desired set pressure is achieved. The locking nut 15 needs to be tightened against the guiding spider 14 without disturbing or moving the set pressure out of tolerance. Usually, the technique involves setting the set pressure of the valve 10 slightly low to accommodate any upward shift in set pressure due to tightening the nut 15. As stated above, this assembly and pressure adjustment process is tedious and time consuming.
In addition, if the valve 10 is not periodically operated, the rubber O-ring 12 has shown a propensity to attach itself to the seat and cause a high (and out of tolerance) first crack. Also, once the fluid begins to flow through the valve 10, the poppet 11 has no means of being guided and can fall over to one side. This causes inaccurate flow and uneven wear on the O-ring 12.
Therefore, a need exists for a better functioning relief valve that is more efficient and economical to manufacture, assemble, and calibrate.